(1) Field of the Invention
The present invention relates to missile stabilization by rotation and relates to rockets having an element rotated by gas discharge.
(2) Description of the Related Art
It is well known to gyroscopically stabilize an elongated body such as a football, bullet, or rocket propelled missile by rotation of the entire body about its longitudinal axis. While it is conceptually possible to achieve such stabilization by rotation of a portion of such a body, insofar as known to the applicant, no such arrangement for gyroscopic stabilization has been deployed to any extent, if at all, despite possible advantages.
For example, in unguided, shoulder launched, recoilless rocket munitions, the current state of the art is rotation of an entire munition around its axis by fins, which pop-out at the tail of the munition, by rifling grooves within a launcher tube engaging the munition, or by fins or cutouts disposed at a rocket nozzle for impingement by rocket exhaust gases.
With these munitions, rocket gas generation must end before the munition has left the launching tube to prevent injury to the operator and is typically in the order of 0.01 second. Also in these munitions, simplicity and low cost are essential, so that no active guidance can be provided and the munition is guided solely by directing its launching tube.
Pop-out fins do not begin to rotate a munition until after it has exited its launcher so that a munition with pop-out fins is subject to misdirection immediately upon exiting the tube as by wind forces, tipping by gravity, or residual unbalanced gas forces. Also, with pop-out fins there are many parts to be assembled; the fins create excess drag; they may engage objects along the trajectory; and the shock of pop-out may damage the munition.
Rifling adds to the weight and expense of the launcher, creates an unbalanced force, and incurs friction losses.
With fins or cutouts for impingement by rocket exhaust, the burn time is extremely short and the entire munition is relatively heavy, a useful amount of rotational inertia cannot be obtained without large internal nozzle features that impede gas flow and cause thrust loss. Also, the munition spins against a launching tube incurring friction losses. Such thrust and friction losses also occur when a munition is rotated by auxiliary nozzles having a circumferential direction.
The advantages of rotating less than all of a munition for gyroscopic stabilization are recognized in U.S. Pat. No. 6,666,144, which issued to Kim et al on 23 Dec. 2003, and in U.S. Pat. No. 2,611,317 issuing to Africano on 23 Sep. 1952. However, in these patents the rotating part has a axial length substantially greater than its diameter and, thus, apparently a relatively high moment of inertia.
U.S. Pat. No. 6,666,144 discloses a rocket motor and warhead system where the warhead is decoupled from the rocket motor so the entire motor can spin separately. The motor is spun by “flutes machined in the rocket nozzle body.” Relative motion between the motor and warhead is provided by annular bearings typically made from a plastic material, such as, polytetrafluoroethylene or “acetal”, and a “dry film lubricant” may be applied to reduce friction. Such a bearing is stated to be less expensive than a ball bearing and to not degrade during storage as do lubricants used with ball bearings. It is apparent that this patent does not disclose decoupling of a portion of a rocket motor from the rest of the motor. Accordingly, the disclosed decoupled motor has a relatively higher moment of inertia than any lesser portion of the motor so that internal nozzle features, which impede gas flow, are required to a greater extent than with such a lesser motor portion.
U.S. Pat. No. 2,611,317 discloses a rocket projectile in which a conical nozzle exit portion is rotationally mounted on the rest of the motor and projectile by a ball bearing at the nozzle throat. The nozzle portion is provided with internal vanes responsive to the flow of propellent gases to rotate the nozzle portion. This patent is restricted to rotating the entire conical, rearward portion of the nozzle. It is apparent that this conical, rearward portion has a relatively higher moment of inertia than any lesser portion of the nozzle or motor so that internal nozzle features which impede gas flow are required to a greater extent than with such a lesser portion.
Also in U.S. Pat. No. 2,611,317, the conical portion is mounted rotationally at the nozzle throat where the temperature and pressure are relatively high with attendant sealing difficulties, particularly at ball bearings having the above-mentioned storage problems. Further, the conical portion is cantilevered from the rest of the motor at the bearing and seal region so that precision fitting and careful balance would be required for maximum effectiveness.